The invention relates in particular to a cladding element for device sections of incinerators that consists of a lower plate made of steel and an upper plate made of steel, which lie one atop the other and are tightly bonded with each other at least in the edge areas, wherein a meandering channel is formed between the lower plate and upper plate for guiding a cooling medium through the cladding element.
Device sections of incinerators, in particular garbage incinerators, are most often exposed to very high loads. These are thermal, chemical and mechanical loads, and frequently combinations thereof, of course. Since garbage incinerators most often make use of moving grates that mechanically convey incineration material into the combustion chambers, especially strong abrasive loads must here be expected, which are amplified even further as a result of high temperatures softening the metal sections. For this reason, the moving parts that are especially threatened in these moving grates, specifically the grate plates of the individual grate steps, are normally designed as medium-cooled hollow bodies. As a rule, water is used as the cooling medium. Cooling reduces the mechanical wear caused by abrasion, and hence of course ends up lowering the cost of maintenance, since the metal parts exposed to wear need to be replaced less often.
EP-0 621 449 shows a method for burning garbage on an incineration grate, as well as an incineration grate that can be used for this purpose. The individual grate plates of the incineration grate have the outward appearance of a board, which is made of sheet metal, and forms a hollow body with an upper and lower side. This hollow body is comprised either of two half-shells or a hollow profile. It has a connecting branch on the one side of the lower side, and a delivery branch on the other side of the lower side for supplying and discharging a cooling medium that flows through the hollow body. In addition, the grate plate extends in its longitudinal direction over the entire width of the incineration grate. Baffle plates can be welded to the interior of the grate plate in such a way as to yield a labyrinthine, meandering channel for the cooling medium.
To ensure that the grate plates of the incineration grate according to EP-0 621 449 are heat resistant, they are made out of a manganese-alloyed sheet metal that is thick enough so still be bendable, for example, meaning having a thickness measuring around 10 mm. In addition, it is also specified that the sheet metal is to have a sufficiently good thermal conductivity, so that no great temperature differences can arise within the grate, making it possible to avoid stresses in the material.
It has been discovered that the water-cooled grate plates according to EP-0 621 449 commonly used today exhibit several disadvantages. For one, the components are heavy and complex, and their production, installation and replacement is associated with a high outlay. Just the high weight of individual grate plates alone requires complicated preparations during repair operations.
It is further known that manganese sheet and manganese steels reach a very high level of hardness, and hence a very high wear resistance, due to their high manganese content, but these materials are also highly susceptible to a change in material properties (embrittlement) upon reheating. Reheating to beyond specific limits results in failure in the course of welding operations (e.g., when manufacturing or repairing such objects), or in cases involving use in incinerators given overheating during operation. In the event of leaks caused by excessive wear, the complex process of replacing entire components is replaced by cutting only the defective partial piece out of the sheet, and welding in a new partial piece, as a result of which this very welding process again entails a risk that the original wear resistance will not be achieved, and the repaired site will consequently have to undergo subsequent and additional repairs.
Since these inherent disadvantages were of course recognized, an attempt was made to find solutions for more easily replacing the wearing parts. One example of an alternative solution is described in WO/2007/107024. This publication discloses a liquid-cooled grate with wearing plates. The grate consists of a liquid-cooled grate plate and a wearing plate that can be placed thereupon. A layer comprised of a thermally conductive material in the form of a highly thermally conductive soft silicone film is advantageously wedged between the grate plate and wearing plate. The silicone film is sued to create a good thermal transfer between the wearing plates and flow-through grate plates. This is intended to ensure that the wearing plates always remain in an uncritical temperature range during operation, because they are cooled by the underlying cooled grate plates, which are approx. 50° C. With respect to the wearing plate, it is specified that a suitable material was one that was sufficiently hard and mechanically resistant, and could be cooled by the underlying plate so as to remain at a temperature that would not compromise its hardness. For example, Hardox steel is specified as a suitable material. Hardox wearing sheets are steel alloys that also contain manganese, in which the strength properties upon delivery cannot be achieved again after heated above a specific temperature limit, for example about 250° C. The stipulated thickness of such wearing sheets measures about 5 to 10 mm.
As a result, the solution according to WO/2007/107024 was still associated with disadvantages similar to those in EP-0 621 449. While it was easier to replace the wearing plates, since very large and heavy parts no longer had to be removed and installed, the dependence on observing certain temperature limits remains in place, because the original wear resistance can only be maintained in this way. Another disadvantage is that any leaks that might nonetheless arise make it necessary to replace not just the wearing plates, but also the underlying, highly thermally conductive films, since these have no comparable wear resistance.
Another solution is known from EP-1 321 711. It depicts an air-cooled grate rod for a moving grate furnace. While a two-plate structure with an upper plate and lower plate is also involved, there is no meandering channel between these two plates, but rather just a cooling gap. In addition, the grate rod is designed as a cast section. As a result, this case also involves a conventional solution, with the disadvantages of a high weight and undifferentiated cooling air distribution, since the cooling air only flows through the cooling gap in the longitudinal direction of the grate rod.
Finally, DE-38 20 448 discloses a cooled wall element for metallurgical furnaces. For example, the disclosed wall element can consist of a metal plate and metal tube half shells welded thereto, wherein a copper layer with a high thermal conductivity is applied onto the metal plate inside the furnace. This copper layer can be applied through weld cladding. However, the basic element structure does not incorporate two metal plates lying continuously over each other, but rather a plurality of individual metal tube half shells in place of the one plate. Therefore, the component is very difficult to manufacture, and also is not provided with an especially wear resistant, but only a readily thermally conductive, inner coating due to the completely different type of application in metallurgical furnaces.